if you have other 3 people investing in your business you
may
have a partnership that requires the filing of form 1065 which was due 3/15/2020. knowing whether or not a partnership return needs to be filed depends on what their investment is. if it's a loan then there should be loan documents specifying the terms including the interest rate. if they're loans you don't have a partnership unless the "interest" they're to be paid is related to the profits. if it is a partnership, it's 5 months late. penalties are potentially in the thousands of dollars. seek out a tax professional that can help you in the return preparation, what has to be done in the future, record keeping, and filing a request for penalty abatement. the money from the investors is not income.